In windows for living rooms the edge surfaces of the brickwork or roof opening are frequently covered with a so-called internal panel member which after the window has been installed is secured to the inward facing edge surface of the main frame, said edge surface being provided, for that purpose, with a groove adapted to receive the edge of the panel. When the width of the groove closely corresponds to the thickness of the panel, securing may be effected by gluing, but a mechanical connection is often preferred--as an alternative or as a supplement--e.g. by means of tightening wedges or screwed ono angle hinges necessitating a tool to be inserted into the generally narrow space between the panel and the edge surfaces of the wall or roof opening. However, the space is frequently so narrow that it is extremely difficult or even impossible to effect such a mechanical securing which shall possibly only serve to keep the panel member in place until the glue has hardened.